Commercial methods for producing dicarboxylic acids generally involve oxidizing naphthenes, cycloaliphatic ketones or cycloaliphatic alcohols with nitric acid in the presence of metal oxidation catalysts.
In the case of adipic acid, specific feed materials such as cyclohexane, cyclohexanol and/or cyclohexanone in admixture with nitric acid are heated at about 40.degree.-140.degree. C. in the presence of a catalyst. The resultant oxidation reaction product comprises adipic acid together with small amounts of monocarboxylic acids and dicarboxylic acids and other organic components in admixture with nitric acid and catalyst components. A substantial quantity of the adipic acid product is recovered by cooling the solution and filtering off the crystallized adipic acid. Oxidation methods of adipic acid production are described in U.S. Pat. Nos. 2,439,513; 2,557,281; 2,719,566; 2,840,607; 2,971,010; 3,338,959; and references cited therein.
In a process involving nitric acid oxidation of cyclohexanone and/or cyclohexanol, economically significant amounts of succinic acid and glutaric acid are formed as byproducts in admixture with adipic acid. After the major portion of the adipic acid is separated by crystallization and filtration, the filtrate mother liquor contains some adipic acid, as well as succinic acid, glutaric acid, nitric acid and metal catalyst values.
Usually this filtrate has been treated as a waste stream. Because of environmental and economic considerations, there has been continuing research effort to develop methods for recovering the valuable and reusable organic and inorganic components of the said filtrate waste byproduct stream.
U.S. Pat. No. 3,726,888 describes a process for the separation and recovery of the components contained in the filtrate waste byproduct stream of an adipic acid manufacturing plant. The filtrate stream comprises a mixture of adipic acid, glutaric acid, succinic acid, nitric acid and metal catalyst values. The separation and recovery process involves contacting the filtrate with alkanol, and extracting with a water-immiscible organic solvent to provide an organic phase containing the formed esters, and to provide an aqueous phase containing the nitric acid and metal catalyst values. Each of the phases is fractionated to separate the mixtures into useful components.
U.S. Pat. Nos. 4,058,555; 4,076,948 and 4,082,788 describe processing improvements which are adapted to overcome some of the difficulties characteristic of the byproduct separation and recovery technology disclosed in the above recited U S. Pat. No. 3,726,888.
U.S. Pat. No. 3,786,096 describes a carboxylic acid recovery process which involves subjecting a mixture of adipic acid and succinic acid to an extraction process wherein an extractant system of water and cyclohexanone and/or cyclohexanol is employed to achieve preferential extraction of adipic acid into an organic phase.
U.S. Pat. No. 3,790,626 describes a method of purifying adipic acid prepared by oxidizing cyclohexane/cyclohexanone/cyclohexanol which method involves subjecting the raw adipic acid crystals to nitric acid treatment, and recrystallizing the treated adipic acid from water.
In U.S. Pat. No. 3,983,208, an aqueous nitric acid solution derived from an adipic acid process containing copper and vanadium catalyst values and dicarboxylic acids is treated to remove the nitric acid and water and yield a substantially dry solid residue. The said solid residue is mixed with a dialkyl ketone solvent which dissolves the dicarboxylic acids and leaves the catalyst metal values as solids.
U.S. Pat. No. 3,991,100 describes a three-step process for making alkyl esters of dicarboxylic acids contained in an adipic acid plant waste stream, which involves distilling the stream to remove water and nitric acid, esterifying the dicarboxylic acids in the residual concentrate, and distilling the esterification product mixture in the presence of a dry base such as sodium carbonate.
U.S. Pat. No. 4,014,903 describes a method of recovering dicarboxylic acids from an adipic acid plant waste stream which involves stripping nitric acid from the waste stream with steam, and thereafter subjecting the nitric acid-free stream to distillation to recover useful products.
U.S. Pat. No. 4,105,856 describes a method for recovering organic and inorganic values from an adipic acid plant waste stream which involves contacting the waste stream with a C.sub.4 -C.sub.20 alcohol to form a water-immiscible ester phase, separating the said ester phase from the aqueous phase, and recycling the aqueous phase to the adipic acid oxidation unit.
Also in connection with treatment of an adipic acid plant waste stream, U.S. Pat. No. 4,146,730 describes a process which comprises the steps of contacting the waste stream with urea to separate out and recover a urea-glutaric acid adduct, contacting the waste stream again to separate out and recover a urea-succinic acid adduct, and thereafter decomposing the adducts to yield the respective dicarboxylic acids.
As indicated by the prior art references described above, investigative effort to recover values from manufacturing plant waste streams is a high priority commitment.
Accordingly, it is an object of this invention to provide an improved process for the recovery of organic acids from dilute aqueous solutions.
It is another object of this invention to provide an improved process for the separation and recovery of dicarboxylic acids and other valuable components contained in a filtrate byproduct stream derived from an adipic acid manufacturing operation involving nitric acid oxidation of cyclohexanol and/or cyclohexanone.
It is another object of this invention to recover catalyst values contained in a filtrate byproduct stream derived from an adipic acid manufacturing operation involving nitric acid oxidation of cyclohexanone and/or cyclohexanol, wherein the recovered catalyst values are contained in an aqueous phase suitable for recycle.
It is a further object of this invention to recover C.sub.4 -C.sub.6 byproducts from an adipic acid manufacturing operation involving nitric acid oxidation of cyclohexanone and/or cyclohexanol, wherein the recovered C.sub.4 -C.sub.6 byproducts are in the form of dicarboxylic acid diesters.